We have determined the complete nucleotide sequence of the integrated proviral genome of avian myelocytomastosis virus (MC29), the complete nucleotide sequence of the chicken c-myc cellular locus and the complete nucleotide sequence of the human c-myc locus. Analysis of the genetic information of these three genes indicates: (i) an intervening sequence in both cellular loci can be identified by consensus splice signals; (ii) the c-myc locus can generate an mRNA whose termination signals are downstream from the translational termination signal; (iii) the three myc genes share the same reading frame, including translational termination signals; (iv) the homology is conserved only in the coding region; (v) most changes at the nucleotide level result in no change in the amino acid; and (vi) there are two distinct domains--the 5' unique domain which is different from the viral, and the 3' coding domain, which contains amino acids coded to the two exons whose sequences have been determined here. In the latter domain, the amino acid variation between v-myc and chicken c-myc is less than 2%, whereas that between the chicken c-myc and the human is 27%, with the variation concentrated in the region that flanks the splice points.